This invention pertains to the field of digital communications systems, particularly to the field of packet transport networking.
List of Acronyms:
CDMACode Division Multiple AccessEOLEnd-of-lineIPInternet Protocol, IETF RFC 791POSPacket-Over-SDH/SONET; used here as to refer any cell, frameor packet based transmission of data over SDH/SONETPPPPoint-to-Point Protocol, IETF RFC 1661SDHSynchronous Digital Hierarchy, ITU-T RecommendationsG.707 and G.783SONETSynchronous Optical NetworkTDMTime Division MultiplexingTCPTransmission Control Protocol, IETF RFC 793WDMWave-length Division Multiplexing
Communication networks today contain packet-switching nodes and circuit-switching transport networks to interconnect the packet-switching nodes. The basic network topology alternatives to interconnect a group of packet-switching nodes that have a substantial amount of data traffic to interchange with each other are full-mesh, packet-ring and star. From the point of view of transporting a packet from one of the interconnected nodes to another one, i.e. from a source node to a destination node among the group of interconnected nodes, these basic alternatives can be defined as follows:                Full-mesh (later also mesh) topology is a transport network that provides direct any-to-any connectivity among the interconnected nodes, i.e. a network where there is a dedicated interconnect path between any pair of the nodes with no intermediate packet-switching nodes along such interconnect paths.        Packet-ring (later also ring) is a network where every one of the interconnected nodes on the ring along the path of a packet between its source and destination node is an intermediate packet-switching node.        Star is a topology where there is always a single intermediate packet-switching node between any pair of source and destination nodes. Unlike the mesh and ring topologies, the star topology requires adding a new packet-switching node (the hub-switch) to the network in addition to the packet-switching nodes interconnected by the network.        
Since every instance of packet-level processing and/or switching along a route of a data packet across a network (like e.g. the Internet) is a potential point of congestion, each intermediate packet-switch node increases the delay, delay variation and the probability of packet discard. Obviously these measures seriously degrade the performance and efficiency of the network both directly and also indirectly, since the communicating applications using e.g. TCP retransmit packets that were not acknowledgedly delivered on time, therefore a portion of network capacity is being wasted for forwarding packets that will not reach their destination in time and that need therefore to be resent. Thus the network efficiency and performance are inversely proportional to the density of packet-switching nodes (called the hop-count in Internet traffic) along the routes across it. Besides the efficiency and performance, also the network cost and scalability need to be considered. In particular, the total interconnect bandwidth requirement, the total port count, and the total amount of packet processing/switching capacity (called later simply packet processing capacity) need to be compared to determine the most cost-efficient packet transport network architecture.
To compare these network cost-efficiency measures, consider a number N [an integer] of packet-switching nodes, each having capacity of A [Gb/s] for interchange of packet traffic with the rest of the interconnected nodes. As it is with e.g. Internet traffic, the demand break-down for the interconnect capacity of A at a given node among the rest of the interconnected nodes may vary in time in an unpredictable and arbitrary fashion, from evenly distributed traffic loads to a case where e.g. the full traffic interchange capacity at a given node is demanded by only one of the interconnected nodes. However, fair sharing of capacity is also required whenever the combined demand for the egress capacity of any given node exceeds A. To support traffic of this nature, the basic network cost parameters with the mesh, ring and star topology alternatives are as follows:
Mesh:
                Interconnect bandwidth requirement R [Gb/s]for N-node full-mesh with guaranteed throughput of A between any pair of nodes in the absence of competing demand for egress capacity at the egress node is: R=N(N−1)A.        (N−1) ports are needed at each node; the total port count P [an integer] is: P=N(N−1).        Requirement for two-directional packet processing capacity per node is (N−1)A, i.e. the total full-duplex packet processing capacity C [Gb/s] in the N-node interconnect network is: C=N(N−1)A.Ring:        The lack of destination-node-performed capacity allocation capability inherent to the packet rings requires that there is a dedicated pipe of A reserved for traffic from each node i.e. R=NA.        Two ports are needed at each node: P=2N.        Requirement for full-duplex packet processing capacity per node is (2R+A). Clearly, R should be greater than A to reduce blocking. SDH/SONET signal rate hierarchy goes in steps of 4, and Ethernet rate hierarchy in steps of 10. Thus in minimum, the packet processing capacity requirement per node (assuming R=4A) is 2×4A+A=18A i.e. in total C=18NA. In case there was a method to size the ring bandwidth to its theoretical minimum Rmin=((N−1)/2)A),C=N(N+1)A.Star:        A pipe of A is needed between each of the N nodes and both of the protected hubs i.e. R=NA+NA=2NA.        A protected hub of N ports is needed in addition to the N nodes: P=2N+2N=4N.        Total requirement for full-duplex packet processing capacity with a protected hub is: C=NA+2×NA=3NA.The above comparison is summarized in the below table:        
Cost FactorMeshRingStarIdealInterconnectN(N − 1)A(N − 1)A/22NA(N − 1)A/2bandwidth (R)Port count (P)N(N − 1)2N4N2NPacket proc. cap (C)N(N − 1)AN(N + 1)A3NANAMax packet processing(N − 1)A(N + 1)ANAAcapacity requirementfor the interconnecttraffic per a singlenodeAver. number of1N/411packet-switchinginstancesCabling (fiber orN(N − 1)L/4LNL/4Lwavelength miles)**as a function of the perimeter L [km] of a 2-fiber ring routed through the sites of the nodes to be interconnected
From the above table it can be seen that many of the key network cost factors bear O(N2) dependency for the number of interconnected nodes, i.e. present the so called N-square scalability problem where a particular cost-measure grows according to the second power of the number of interconnected nodes. Comparable to the N-square scalability problem are cost factors with O(N×A)-dependency, i.e. cost factors that grow according to the product of the traffic exchange capacity (A) per a node and the number of nodes (N). These major factors limiting cost-efficient scalability of networks, per topology class, are:                The mesh topology has the N-square scalability problem associated with all cost measures but the density of packet-switching instances.        The packet ring has an N-square dependency associated with the packet processing capacity requirement.        The maximum packet processing capacity per a single node-requirement with all the basic topologies grows according to the product of the number of nodes (N) and the traffic exchange capacity per node (A).The ‘Ideal’ model is included in the comparison as a reference to show how the traditional alternatives deviate from the theoretical optimum interconnect network, which is implementable according to the innovation description of this patent application. It appears that the implementable theoretical optimum interconnect network minimizes the all the cost measures to less than or equal to those of the traditional topology alternatives, and, in particular, removes all the N-square dependencies and significantly reduces the linear N-dependencies. The deviation of the cost factors of the basic topologies from the Ideal reference is shown in the below table, in which the entries are the cost factor equations of the basic topologies divided by the corresponding Ideal reference equations:        
Cost FactorMesh:IdealRing:IdealStar:IdealInterconnect2NRound-up to the4N/(N − 1)bandwidth (R)closest availablering ratePort count (P)(N − 1)/212Packet proc. cap (C)N − 1N + 13Max packetN − 1N + 1Nprocessing capacityrequirement for theinterconnect trafficper a single nodeAver. number of1N/41packet-switchinginstancesCabling (fiber orN(N − 1)/41N/4wavelength miles)*
Based on the above comparison of traditional topology alternatives, an ideal network providing interconnectivity for a group of packet-switching nodes can be characterized as a system that:                For best performance, shall provide protected non-blocking fully meshable interconnectivity without introducing intermediate packet-switching instances along the paths of packets across the interconnect network;        For most efficient interfaces at the interconnected nodes, shall appear to the interconnected nodes as if they were interconnected using a single hub in star topology; and        To provide protected connectivity with minimum required cabling and transport capacity, shall be able to be implemented using a dual-fiber ring physical topology with the theoretical minimum ring interconnect bandwidth of R=((N−1)/2)A.It is obvious that with the traditional topology alternatives, which are based on non-adaptive connections, the ideal inter-connect network model is not feasible. It is however not theoretically impossible to realize an embodiment of the above ideal model such that:        Is a distributed version of the hub of the star topology so that the interface units of the thus distributed hub-switch are located along the fiber ring that interconnects the packet-switching nodes; and        Provides fall-mesh interconnectivity over the fiber ring among the aforesaid interface units with real-time optimization of allocation of the block (A) of the ring transport capacity reserved for transport of data towards each one of the interface units.Obviously innovative system theory and architecture and novel signaling schemes and algorithms are required in order to realize an embodiment of the ideal interconnect network model. In particular, a novel control scheme is required for performing the network-scope real-time traffic-load-adaptive transport capacity optimization function necessary to provide full-mesh connectivity without creating N-square interconnect bandwidth requirement problem. It in particular is this novel real-time mesh connection control scheme that enables implementing an embodiment of the above characterized ideal interconnect network, and that differentiates the present invention from prior art. With conventional technologies, even connections that carry variable-bandwidth packet traffic have to be provisioned by the network operator, whereas the present innovation provides an automatic algorithm for real-time traffic-load-driven capacity allocation and connection modification process that continuously maximizes the network throughput.        
Since the traditional alternatives are significantly less cost-efficient than the ideal model, especially for higher number of interconnected packet-switching nodes, there clearly is an increasing demand for networks that are close to the above described ideal model. This demand is created especially by the ongoing expansion of the Internet, including rapid growth in the number of Layer 3/2 (IP, MPLS. Ethernet etc) routers/switches that need cost-efficiently scalable high-performance interconnectivity.